I watched "Blood and Sand" and "Gods of the Arena". Good story, good script, good actors (John Hannah is great, some people complained that he didn't moderate his Scottish accent, but WTF, the series is in English, and I'm pretty sure English wasn't invented when the real Spartacus was a gladiator).
There's equal opportunity nudity, with reasonably equal viewings of willies and lady bits. So it's fun for the whole family and every sexual persuasion. The violence is also no holds barred. All that would be shit if the story, script and acting wasn't up to scratch. So IMO it all comes together nicely. I'm pretty sure some of the characters come together too.
I agree that you should not miss the prequel. It helps to flesh out the characters (excuse the pun). And I'm pretty sure they'll write Gannicus' Character into Vengeance (on the Starz website they have hsi character in the cast list for Vengeance) and if you go from Blood and Sand straight to Vengeance you'll have no context for how he's connected to the other characters, esp his friendship with Oenomaus.
“The fundamental cause of the trouble is that in the modern world the stupid are cocksure while the intelligent are full of doubt.” - Bertrand Russell
"When the power of love overcomes the love of power, the world will know peace."
Jimi Hendrix